Magnetic disks and disk drives are conventionally employed for storing data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducing heads positioned in close proximity to the recording surfaces of the disks and moved generally radially with respect thereto. Magnetic disks are usually housed in a magnetic disk unit in a stationary state with a magnetic head having a specific load elastically in contact with and pressed against the surface of the disk.
Data are written onto and read from a rapidly rotating recording disk by means of a magnetic head transducer assembly that flies closely over the surface of the disk. It is considered desirable during reading and recording operations to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the fly height of the head. This objective becomes particularly significant as the areal recording density increases. The areal density (Gbits/in2) is the recording density per unit area and is equal to the track density (TPI) in terms of tracks per inch times the linear density (BPI) in terms of bits per inch.
The increasing demands for higher areal recording density impose increasingly greater demands on flying the head lower. Generally speaking, the lower the HMS, where HMS is the space between the head and the media, the higher the recording density. For example, the output voltage of a disk drive (or the readback signal of a reader head in disk drive) is generally proportional to 1/exp(HMS). Therefore, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk to be positioned in closer proximity with an attendant increase in predictability and consistent behavior of the air bearing supporting the head.
Most of the current magnetic disks are normally driven by the contact start stop (CSS) method, while many advanced disk drives, especially for lap top computers, are using the load/unload ramp design mechanism.
In the load/unload ramp design, the head is parked off the disk when the disk drive is not in use. This is conventionally done by the use of a load and unload ramp, wherein a load and unload tang of a head suspension assembly slides along, thereby moving the head between a position on the disk and a position parked off the disk.
In the CSS method, the head begins to slide against a landing zone of the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk landing zone. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates. The magnetic head unit is arranged such that the head can be freely moved in both the circumferential and radial directions of the disk in this floating state allowing data to be recorded on and retrieved from the surface of the disk at a desired position.
Upon terminating operation of the disk drive; the rotational speed of the disk decreases and the head begins to slide against the surface of the disk again and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from a stop and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk and stopping.
As explained above, as the fly height of magnetic hard disk drives continues to decrease, the product drive head-disk-interface (HDI) flyability is becoming increasingly dominated by the dynamic interaction between the head air bearing resonance characteristics and disk micro-waviness. Indeed, most of the drive-level flyability failures that we are facing now are directly resulted from the excessive HMS modulation. Therefore, controlling magnetic disk micro-waviness is a critical step in ensuring a good reliability of the magnetic hard disk drives.
U.S. Pat. No. 6,568,252 deals with how to establish the point of contact as a base line that indicates the location of the disc surface, and once the base line is established, how to fly the glide head with greatly increased precision at the desired glide height. U.S. Pat. No. 6,026,676 discloses how to determine the glide avalanche break point. U.S. Pat. No. 5,237,861 relates to a disk inspection apparatus for inspecting protuberance on the disk surface that includes an inspection head detecting the protuberance by a piezoelectric sensor and a rotating speed control circuit controlling a rotating speed of the magnetic disk.
The present invention describes a method for measuring very small changes in recorded signals on a spin-stand tester and a system therefore. Particularly, this invention focuses on correcting sensitivity changes of the transducer. The present invention deals with a technique that allows the measurement of signal changes much more sensitively than that possible by the prior art methods. In addition, data could be acquired one order of magnitude faster than that done using the prior art methods.